Taxonomy & naming
Nomorhamphus sanussii was described by Brembach in 1991 from material collected in southern Sulawesi, Indonesia. It belongs to the genus Nomorhamphus, the viviparous halfbeaks of the family Zenarchopteridae (order Beloniformes) — the internally fertilising halfbeaks, set apart from the egg-laying marine and estuarine halfbeaks of the Hemiramphidae. The genus name combines the Greek roots for "filament" or "thread" and "bill" or "beak", a reference to the beak-like extension of the lower jaw that defines the halfbeaks, here shorter than in many relatives.
The species' status is genuinely contested, and this matters for an atlas that follows Eschmeyer's Catalog of Fishes for valid names. Catalog of Fishes carries Nomorhamphus sanussii as a named species (CoF species id 60285). FishBase, however, follows Meisner's 2001 revision of the internally fertilised halfbeaks and treats N. sanussii Brembach, 1991 as a junior synonym of the senior name Nomorhamphus brembachi Vogt, 1978, flagging its summary page for removal. Both names trace to the same southern-Sulawesi region, and the two are very likely the same biological entity under different names.
Readers should treat this page as provisional: if the synonymy under N. brembachi is upheld as the prevailing usage, the valid scientific name for this fish becomes Nomorhamphus brembachi Vogt, 1978, with sanussii falling as a junior synonym. The atlas retains the Brembach name here because it is the name under which the fish was searched and catalogued, but the underlying animal is best understood as part of the brembachi complex of southern Sulawesi halfbeaks.
Morphology
Nomorhamphus sanussii is a small, elongate, surface-living fish. FishBase records a maximum length of about 3 in SL for N. sanussii, while the senior synonym N. brembachi is listed at around 2.5 in SL — figures consistent with a slender halfbeak of a few centimetres rather than a large fish. The body is pencil-shaped and built for life just beneath the surface film, with the dorsal and anal fins set well back toward the tail in the typical halfbeak arrangement.
The defining feature of the genus, and of the halfbeaks in general, is the jaw. In Nomorhamphus the lower jaw is extended into a short beak, but markedly shorter than the long, needle-like lower jaw of the related genus Dermogenys — a distinction hobbyists use to separate the two. This shorter beak gives Nomorhamphus a stubbier profile at the head.
Detailed species-specific morphometrics, fin-ray counts and colour descriptions for N. sanussii are sparse in the accessible literature, in part because of its uncertain standing as a synonym of N. brembachi. As with other Nomorhamphus, the sexes differ: males are typically the smaller sex and carry a modified anal fin (the andropodium) used in internal fertilisation, while females grow larger and deeper-bodied, particularly when gravid.
Habitat
The species is endemic to southern Sulawesi, Indonesia, and is known from freshwater streams in that region. FishBase classifies it as a tropical freshwater, pelagic fish — that is, one that lives in the open water column rather than on the bottom — occupying the upper layers near the surface where its beak-feeding habit is most effective.
The halfbeaks of Sulawesi as a group are associated with cooler, well-oxygenated, often flowing waters rather than the warm, still conditions favoured by many tropical livebearers. Aquarium accounts of the genus repeatedly note a preference for relatively cool water and good current, reflecting the upland and stream habitats from which these fishes come. Sulawesi's freshwater fauna is famous for its high endemism, and these halfbeaks are part of that distinctive island assemblage.
Precise water chemistry, depth and seasonal data for the streams inhabited by N. sanussii are not available in the sources at hand; the habitat picture here is assembled from the genus and from the general character of southern Sulawesi's running waters, and should be read as indicative rather than measured for this species.
Feeding
Nomorhamphus halfbeaks are surface-oriented micro-predators. The beak-like lower jaw and upward-facing mouth are adaptations for taking small prey at or just below the water surface, and FishBase places the species at a trophic level of roughly 3.1, the value expected of a small insectivore rather than a herbivore or top predator.
In practical terms this means a diet dominated by small insects and insect larvae taken from the surface film, supplemented by other small drifting invertebrates. Hobby accounts of the genus describe the fish hanging just under the surface and snapping at items that fall onto or move across the water, behaviour entirely in keeping with the halfbeak body plan.
In captivity, Nomorhamphus are accordingly best fed small foods at the surface — small live and frozen items such as Daphnia, mosquito larvae, and similar invertebrate foods, along with floating or slow-sinking prepared foods that they can take before the items leave the upper layer. No diet study specific to N. sanussii is available, so this account follows the well-established feeding habits of the genus.
Mating
Unlike the egg-laying halfbeaks of the family Hemiramphidae, the Zenarchopteridae — including Nomorhamphus — practise internal fertilisation, and Nomorhamphus is viviparous, giving birth to live young. Fertilisation is achieved by the male transferring sperm to the female using a modified anal fin. In the poeciliid livebearers this intromittent organ is called the gonopodium; in the halfbeaks the equivalent modified anal-fin structure is generally termed the andropodium, but the principle is the same — the male inseminates the female internally rather than fertilising shed eggs externally.
Females of the genus grow larger than males, and courtship in these surface fishes centres on the male approaching and positioning alongside the female to bring the andropodium into contact for sperm transfer. As internally fertilising livebearers, females may be able to carry developing young while a clutch matures, but the published evidence specific to N. sanussii is too thin to assert details such as sperm storage or superfetation for this species in particular.
Where the poeciliid guppies and mollies are the textbook models for live-bearing mating systems, the Sulawesi halfbeaks are a much less studied parallel experiment in internal fertilisation within a different fish order — and N. sanussii, caught up in a synonymy with N. brembachi, is among the more obscure of them.
Breeding
Nomorhamphus are livebearers: after internal fertilisation the female carries the developing embryos and gives birth to free-swimming young rather than depositing eggs. Genus-level aquarium accounts report that females give birth at intervals of roughly four to six weeks, producing successive broods of comparatively large, well-developed fry — a livebearer strategy of fewer, bigger young than the egg-scattering fishes that share their waters.
The newborn young are sizeable relative to the parents and are capable surface feeders from birth, taking small live foods immediately. As with most livebearers, providing cover and feeding the adults well reduces predation on the fry. Brood sizes for halfbeaks tend to be modest — a handful to a few dozen young — rather than the large broods of a prolific guppy, though no figure specific to N. sanussii is documented in the accessible sources.
Gestation length, brood size and birth interval cited here are drawn from the genus rather than measured for N. sanussii itself, which has no dedicated reproductive study in the material reviewed. The broad pattern — internal fertilisation, gestation of a few weeks, and live birth of large fry at intervals — can be stated with confidence; the precise numbers cannot.
In the aquarium
Sulawesi halfbeaks are uncommon, somewhat specialised aquarium fish rather than beginners' livebearers. They are wild-caught and rarely traded, so they reach hobbyists only sporadically, usually through specialists in oddball or livebearer fishes. N. sanussii in particular is obscure even by that standard, frequently subsumed under the name N. brembachi.
The key husbandry points come from the genus. These are surface fishes that benefit from a covered, calm-surfaced but well-oxygenated tank with some current, and from cooler water than most tropical community fishes — genus guidance points to roughly 68–75 °F, with neutral to slightly alkaline water (pH above 7). They are nervous, surface-dwelling fishes prone to dashing, so a secure cover and unhurried tankmates suit them. Small surface-taken foods, fed regularly, keep them in condition.
Given the sparse species-specific data, an aquarist keeping this fish is effectively keeping a southern-Sulawesi Nomorhamphus and should follow general halfbeak care: cool, clean, oxygenated water; a tight lid; live and frozen surface foods; and patience with a wild-caught oddball that does not always settle quickly. This is a fish for the dedicated livebearer enthusiast rather than the general community keeper.
Conservation
Nomorhamphus sanussii has not been evaluated by the IUCN Red List; its status is Not Evaluated (NE). There is no dedicated Red List assessment page for the species, and CITES and CMS likewise list it as not evaluated. The likely senior synonym, N. brembachi, is also unassessed, so no formal conservation status is available under either name.
The absence of an assessment should not be read as evidence that the fish is secure. The species is a narrow-range endemic confined to streams in southern Sulawesi, and small, range-restricted island endemics of this kind are inherently vulnerable to habitat alteration, pollution and water abstraction. Sulawesi's freshwater fauna more broadly faces such pressures, and a fish known from a limited area warrants caution by default.
For the aquarist, the responsible position is to treat wild-caught Sulawesi halfbeaks as a finite resource: prefer captive-bred stock where it can be obtained, support efforts to establish self-sustaining aquarium populations of these poorly known livebearers, and never release aquarium fish into local waters. With the species' very taxonomy unresolved, even basic conservation accounting is hampered — a reminder that obscure, narrowly distributed fishes can slip through the gaps of formal assessment entirely.